Go to Site Administration > Plugins > Plugins Overview and click Uninstall next to the Jabber messaging processor.
Go through the uninstallation process. Check that no strict standards warning are displayed.
Go to Site Administration > Notifications to reinstall the Jabber processor.

Description

This appeared during the un-installation of a message processor. Site Administration > Plugins > Plugins Overview), scroll down to Messaging processors. Click uninstall. I uninstalled the Jabber processor. Not sure if that is significant.

Ruslan Kabalin
added a comment - 02/May/12 7:03 PM Added commit to fix it. Since MDL-32009 is not on public master yet, I add fix to this branch. It can be cleanly cherry-picked to master once the MDL-32009 is released.

Eloy Lafuente (stronk7)
added a comment - 12/May/12 1:31 AM This is now part of Moodle and a few millions people around the globe will be using it soon. Isn't that awesome?
Many, many thanks and don't forget http://youtu.be/4N7dPaP5Z8U
Closing, ciao